Assessing the Health of U.S. Forests

Annual report details conditions across all 50 states

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Scientists from across the Forest Service, as well as university researchers, state partners, and other experts contributed to the 2018 FHM report.

Forests are complex ecosystems. They are constantly changing as a result of tree growth, variations in weather and climate, and disturbances from fire, pathogens, and other stressors.

The USDA Forest Service Forest Health Monitoring (FHM) program tracks these ongoing changes — every year, across the nation — as a forest health check up.

The 2018 FHM report is the only national summary of forest health undertaken on an annual basis. It contains short- and long-term forest health assessments for the continental U.S., Alaska, Hawaii, Puerto Rico, and the U.S. Virgin Islands.

The report is available as a General Technical Report. Individual chapters can be downloaded, and the full series of FHM annual reports is also available. Users can search reports and chapters by year or topic. Highlights and additional resources are also included.

Kevin Potter, a North Carolina State University scientist supported by the Southern Research Station, edited the 2018 report with fellow NCSU scientist Barbara Conkling.

The report identifies ecological resources whose condition is deteriorating, potentially in subtle ways, across large regions. This requires consistent, broad-scale, and long-term monitoring of forest health indicators — and the participation of multiple federal, state, academic, and private partners.

“The FHM reports represent a solid partnership between universities, Forest Service Research, and State and Private Forestry,” notes Tom Eager, FHM national program manager.

Frank Koch, who represents Research on the FHM Management Team, adds that the reports are important, “because they provide a way to present research results in a timely and client-oriented way.”

Notable highlights from the 2018 report include:

  • In 2017, 63 different mortality-causing insects and diseases were detected on nearly 8.1 million acres across the lower 48 states. Fifty defoliation-causing insects and diseases were detected on close to 120 million acres. Emerald ash borer was the most commonly detected cause of tree mortality in the East, while a variety of bark beetle species – especially fir engraver, western pine beetle, spruce beetle, and mountain pine beetle – were major causes of mortality in the West.
  • Much of the southwestern U.S. and portions of southern California were affected by extreme drought conditions in 2017. Parts of the central Midwest, the northern Great Plains, and the Southeast experienced moderate to severe drought.
  • The number of satellite-detected forest fire occurrences in 2017 was the fifth highest since the beginning of data collection in 2001 and the highest since 2014. Areas in the Pacific Northwest, the northern Rocky Mountains, and California had the highest density of forest fire occurrences.
  • Analysis of Forest Inventory and Analysis (FIA) data revealed that tree mortality is low relative to growth in most of the central and eastern US, with areas of the highest mortality found in riparian forests of the Great Plains. In contrast, mortality exceeded growth throughout much of the forest of the Pacific Coast states, especially in southern California.
  • Additional analyses of FIA data on invasive plants in the eastern US showed that half of the total area of 74 different forest types was invaded. Plant invasions were almost twice as likely on privately owned land than on public lands.
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Research on the bishop pine (Pinus muricata) shows a convergence of multiple stressors, including invasive pathogens and changes in seasonal water availability. Photo courtesy of Christopher Lee, California Department of Forestry and Fire Protection.

The report also presents results from three FHM-funded studies of declining forest health in areas of special concern. Those chapters focus on the decline of bishop pine in California’s northern coast; the infestation of the Hawaiian native naio tree by an invasive insect; and the impact of rising temperatures on Great Basin bristlecone pine forests in Nevada and Utah.

“The U.S. is big, and its forests are quite different in different parts of the country,” says Potter. “So, the threats that forests face also vary from place to place. Most of our forests face at least one threat, whether that’s fire or an invasive insect pest or competition from nonnative plants.”

Potter, Conkling, and the other authors have completed a draft of the 2019 FHM report and expect its publication in the summer of 2020.

Read the full text of the report.

For more information, email Kevin Potter at kevin.potter@usda.gov.

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